Printing of Soft Neural Interface Systems on the Cranium for Wireless Neural Recording

Unveiling the mechanism of the functional connectivity of the brain can help reveal the treatments for brain dysfunction causing brain disorders and neurodegenerative diseases. Thus, long-term monitoring of brain activities with high-spatiotemporal resolution in natural conditions of subject is necessary. Moreover, current approaches for wireless neural recording based on battery-powered or battery-free systems, deteriorate integration to the biological system by requiring replacement of intermittent batteries and heavy batteries mounted on the head, or additional bulky stages for wireless power transfer and data acquisition system.<br/>To overcome these limitations, we report a soft, conformable, and printable neural interface system on the cranium for wireless neural recording that can be conformally integrated within the subject’s head, with the high-resolution printing of eutectic gallium-indium alloy (EGaIn; 75.5% gallium, 24.5% indium by weight), which is a representative gallium-based liquid metal. The printed neural interface system comprises soft neural probes, cranial circuits, and form factor-free batteries. First, liquid metal-based neural probes are fabricated structurally and mechanically similar to neurons (~ 5 um), minimizing the formation of inflammation and immune responses. Second, liquid metal-based cranial circuits are directly printed on the surface of the cranium for electrical connection to neural probes, which are implanted in multiple brain regions of a single subject, with adaptable geometries. Third, liquid metal-based electrical interconnections with subsidiary electronics form miniaturized and conformal circuits on the cranium within the subject’s head, which maximizes the integrity of electronics to biological systems, minimizing bulky head-mounted configurations. Furthermore, in-vivo recording using our device in freely moving mice demonstrated the simultaneous recording of local field potentials (LFPs) and single-unit spiking in multiple regions of the brain, as well as its biocompatibility and stability for the long term (~ 33 weeks), and these results suggest its broad and practical applications for various bioelectronics and neuroscience research.